Heretofore, numerous compounds and catalysts have been used for the preparation of polyester resins. However, high clarity, neutral hue, and low haze polyester articles such as films, sheets, containers, and the like are desirable, especially for containing food or drink, or when replacing glass. Often, antimony has been used as a catalyst, at times in combination with a phosphite compound. However, the reaction between these two compounds would often result in some amount of antimony metal being formed which imparted a gray color to the resin and article formed therefrom. Moreover, if other catalysts were utilized, a high level of acetaldehyde was produced which is highly undesirable for use in connection with food containers.
U.S. Pat. No. 3,795,639 to Chimura, et al relates to a process for preparing linear polyesters wherein the polycondensation of glycol terephthalate is preformed in the presence of (1) an antimony catalyst, (2) a germanium compound and (3) a phosphoric ester. This patent is not pertinent in that it does not utilize a bluing agent and does utilize a germanium compound.
U.S. Pat. No. 3,732,182, to Chimura, et al is not pertinent in that it relates to a novel antimony compound having the formula Sb(OR.sub.1)(OR.sub.2)(OR.sub.3).
U.S. Pat. No. 3,965,071 to McClelland relates to the preparation of polyesters in the presence of a titanium compound, the deactivation of a catalyst by reaction with phosphoric acid or ester and polycondensation in the presence of an antimony compound. Thus this patent relates to a completely different catalyst system as well as to a deactivation of the titanium catalyst.
U.S. Pat. No. 3,842,043 relates to a white, transparent polyester utilizing a polycondensation catalyst solution containing germanium dioxide, glycol and a solubilizing agent such as calcium, magnesium, strontium and zinc metals or salts thereof. Hence, it is not pertinent.
U.S. Pat. No. 4,082,724 to Hewertson relates to polyesters containing a trihalide or a tri(pseudohalide) of antimony and an organic oxo compound of phosphorus. The mole ratio of the oxo phosphorus compound to antimony is generally in excess of 1.0. This patent is not pertinent in that it uses very high amounts of phosphorus compounds and does not utilize a bluing agent.
An article of Unitika Co., Plasdoc 31808 V/17 Dewent Publications (April 1, 1974), obtains a polyester by polymerizing a bis(W-hydroxyalkyl)terephthalate and/or its oligomer in the presence of an antimony compound, a cobalt compound, and a halide phosphate compound. This article is not pertinent in that a halide phosphate compound is utilized and relates to making polyesters from dimethyl terephthalate.
U.S. Pat. No. 3,962,189 to Russin et al, 3,907,754 to Tershansy et al, and 4,010,145 to Russin et al are all very similar in that they relate to catalyst inhibitor systems having a combination of organic or inorganic salts of manganese and cobalt, titanium compounds, antimony compounds, and a phosphate ester. The amount by weight of phosphorus is greater than the total weight of cobalt, manganese, and titanium. Moreover, the examples generally show the amount of phosphorus being at least four times as much as the amount of cobalt. Thus, these references are not pertinent in that they use very high amounts of phosphate in comparison to the other metals, as well as use other components not utilized by the present invention. Moreover, they relate to making a polyester from dimethyl terephthalate and not from dicarboxylic acids.
U.S. Pat. No. 2,641,592, to Hofrichter, relates to a cobalt acetate catalyst in association with antimony for the polymerization of dimethyl terephthalate. This patent is not pertinent in that it lacks any suggestion utilizing any phosphate compound. Additionally, such a composition would yield unacceptably high acetaldehyde levels in containers made therefrom.
U.S. Pat. No. 3,028,366 to Engel et al relates to phosphate modifiers in association with antimony catalysts to produce colorless or white polyesters from dimethyl terephthalate. In passing, the patent states that other well known catalysts or catalyst combinations can also be utilized including various metals such as calcium, magnesium, lanthanum, manganese, and cobalt. Since such compounds are utilized as catalysts, high amounts thereof are required. This patent is not pertinent in that it fails to specifically teach applicant's use of a bluing agent, very small amounts of phosphate in comparison with any bluing agent as well as small amounts of the bluing agent, and relates only to the use of dimethyl terephthalate.
The above patents and articles all generally relate to the utilization of dimethyl terephthalate in preparing the polyester. Whenever various catalysts are utilized such as manganese, cobalt and the like, relatively high amounts, that is generally in excess of 70 parts per million by weight of the element must be utilized. Such compounds necessarily impart a color to the polyester, for example a blue color, and hence are inherently incapable of producing a neutral hue polyester artile, that is a colorless or transparent article, with low acetaldehyde content and generation rate.